In the related art, a wiring substrate for mounting thereon electronic components such as a semiconductor chip and the like has been known. In an example of the wiring substrate, a copper post is erected on a pad of the wiring substrate, the semiconductor chip is flip chip-connected to the copper post, and an underfill resin is filled between the semiconductor chip and the wiring substrate.
Patent Document 1: JP-A-2007-103878
As described later in paragraphs of preliminary matters, linear thermal expansion coefficients are different between the copper post of the wiring substrate and the underfill resin. For this reason, when the underfill resin is subjected to heating processing, a gap is likely to be generated between a side surface of the copper post and the underfill resin due to deformation resulting from thermal shrinkage of the underfill resin.